1. Field of the Invention
The invention relates to the conversion of ethanol to propylene. More particularly, it relates to the direct conversion of ethanol to propylene using a modified ZSM-5 zeolite catalyst.
2. Background of the Art
Propylene is an important starting material for a wide range of materials used in producing both durable and nondurable goods. While its price is currently subject to significant fluctuation, there remains an industrially important supply and demand market at a level of millions of metric tons (billions of pounds) per year.
Propylene is most typically produced as a by-product of either ethylene production or refinery operations. Where it is produced in connection with ethylene production, a steam cracking process uses heat to produce a mixture of hydrocarbons, and specific products, such as propylene, may then be isolated by distillation. Significant quantities of propylene are produced when naphtha is used as the steam cracking feedstock. Where it is produced as a by-product of refinery operations, catalytic cracking of heavier petroleum fractions may be carried out. Unfortunately, the fact that both of these routes begin with petroleum, which is subject to supply and price fluctuations, the cost of producing propylene, and therefore the demand for it, likewise varies. This makes it difficult for producers to maintain acceptable margins and anticipate future demands. Because of these issues, alternative starting materials for propylene production have been sought.
In recent years much research has gone into methods to produce desirable hydrocarbon products from renewable sources, such as biomass that results from fermentation. Such sources include various plants, including, for example, sugar cane. Production of ethanol from such sources has been highly successful. Because of this success, the possibility of producing propylene from bio-resourced ethanol has arisen. However, most known methods suffer from relatively low propylene yield. Identification of ways to increase propylene yields from ethanol are therefore now highly desired.